1. Field of This Invention
The present invention relates to a method for the production of mineral fibers which are resistant to alkaline media and to be used for the micro-reinforcement of cement-, lime- and/or plaster-bound or bituminous binders of building materials. Further subject matters of this invention are the composition of the fibers and the aftertreatment to increase their bond strength.
2. Prior Art
The range of application of many building materials, such as cement, concrete, plaster, lime or others, is strongly restricted by their low tensile strength, bending strength and impact strength. It is well known that the above properties can be improved by so-called micro-reinforcement, i.e. by the addition of fibrous materials used for this purpose which are either natural fibers, such as asbestos or plant fibers, or artificial fibers made from steel, glass, organic polymers or carbon. The examination of these fibers for their suitability as reinforcing material for cement-, plaster- and lime-bound as well as bituminous building materials so far has furnished unsatisfactory results in most of the cases. Aspects of major importance in this context are environmental implications, e.g. of the use of asbestos, and material-specific problems.
Even the commercially available glass fibers which were initially regarded as suitable in the end turned out to be insufficiently resistant to alkaline media, which means that they lose their favorable mechanical properties, in particular their tensile strength, as a result of the corrosion starting on the surface of the glass fibers in cement-bound building materials.
To protect the glass fibers from being attached by the alkaline solution, they have already been provided with alkali-resistant coatings. This, however, was not an effective measure to prevent either attack at fiber fracture surfaces or at defects in the protective coating. Another serious drawback was that the protective coating reduced the bond strength of the fibers in the binder matrix; as a result, the intended reinforcing effect of the fibers was not achieved, and the mechanical properties were substantially impaired.